The present invention relates to a protable radiophone, and in particular to a slot antenna device adoptable to an interior of a portable radiophone.
A portable radiophone employs basically a monopole antenna device utilizing a vertical polarized-wave or else a patch antenna device combined therewith. In the latter case, since the patch antenna is narrow in bandwidth and low in gain, it is utilized mainly for receiving only, while the monopole antenna or a whip antenna device is utilized for both transmitting and receiving. The monopole and whip antennas are antennas which are projected outward of a portable radiophone, which require a length more than at least 1/4 wave length in order to obtain enough antenna efficiency therefrom. However, since such an antenna has an externally projected form, it can be often damaged and inconvenient for carrying, and its antenna gain also has limitation due to its limited antenna size. Moreover, since the portable radio telephone should be often used in a tilted position of apparatus, a slant vertical-polarized wave is to be transmitted and received through its antenna. However, since the external antenna is an antenna utilizing the vertical polarized wave, sensitivity deteriorates at about horizontal position of the antenna, thereby giving a problem that an effective transmitting and receiving of radio signals may not be made through the antenna.